ForCES Model Extension
draft-ietf-forces-model-extension-03

Internet Engineering Task Force                            E. Haleplidis
Internet-Draft                                      University of Patras
Updates: 5812 (if approved)                                 July 4, 2014
Intended status: Standards Track
Expires: January 5, 2015

                         ForCES Model Extension
                  draft-ietf-forces-model-extension-03

Abstract

   Forwarding and Control Element Separation (ForCES) defines an
   architectural framework and associated protocols to standardize
   information exchange between the control plane and the forwarding
   plane in a ForCES Network Element (ForCES NE).  RFC5812 has defined
   the ForCES Model that provides a formal way to represent the
   capabilities, state, and configuration of forwarding elements within
   the context of the ForCES protocol, so that control elements (CEs)
   can control the FEs accordingly.  More specifically, the model
   describes the logical functions that are present in a forwarding
   element (FE), what capabilities these functions support, and how
   these functions are or can be interconnected.

   RFC5812 has been around for two years and experience in its use has
   shown room for small extensions without a need to alter the protocol
   while retaining backward compatibility with older xml libraries.
   This document update RFC5812 and extends the model to allow complex
   datatypes for metadata, optional default values for datatypes,
   optional access types for structures and fixes an issue with LFB
   inheritance.  The document also introduces two new features a new
   event condition BecomesEqualTo and LFB properties.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

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   This Internet-Draft will expire on January 5, 2015.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     1.2.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  ForCES Model Extensions . . . . . . . . . . . . . . . . . . .   4
     2.1.  Complex datatypes for Metadata  . . . . . . . . . . . . .   4
     2.2.  Optional Default Value for Datatypes  . . . . . . . . . .   5
     2.3.  Optional Access Type for Structs  . . . . . . . . . . . .   8
     2.4.  New Event Condition: BecomesEqualTo . . . . . . . . . . .  10
     2.5.  LFB Properties  . . . . . . . . . . . . . . . . . . . . .  11
     2.6.  LFB class inheritance . . . . . . . . . . . . . . . . . .  13
     2.7.  Enhancing XML Validation  . . . . . . . . . . . . . . . .  14
   3.  XML Extension Schema for LFB Class Library Documents  . . . .  14
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  28
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  28
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  28
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  28
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  28
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  29
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  29

1.  Introduction

   The ForCES Model [RFC5812] presents a formal way to define FEs
   Logical Function Blocks (LFBs) using the eXtensible Markup Language
   (XML).  [RFC5812] has been published a more than two years and
   current experience in its use has demonstrated need for adding new
   and changing existing modeling concepts.

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   Specifically this document updates the ForCES Model [RFC5812] to
   allow complex datatypes for metadata (Section 2.1), optional default
   values for datatypes (Section 2.2), optional access types for
   structures (Section 2.3) and fixes an issue with LFB class
   inheritance (Section 2.6).  Additionally the document introduces two
   new features a new event condition BecomesEqualTo (Section 2.4) and
   LFB properties (Section 2.5).

   These extensions are an update to the ForCES model [RFC5812] and do
   not require any changes on the ForCES protocol [RFC5810] as they are
   simply changes of the schema definition.  Additionally backward
   compatibility is ensured as XML libraries produced with the earlier
   schema are still valid with the new one.  In order for XML libraries
   produced by the new schema to be compatible with existing ForCES
   implementations, the XML Libraries MUST NOT include any of the
   features described in this document, else the old implementation will
   be unable to parse the XML library.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

1.2.  Definitions

   This document uses the terminology defined in the ForCES Model in
   [RFC5812].  In particular, the reader is expected to be familiar with
   the following terms:

      FE Model

      LFB (Logical Functional Block) Class (or type)

      LFB Instance

      LFB Model

      Element

      Attribute

      LFB Metadata

      ForCES Component

      LFB Class Library

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2.  ForCES Model Extensions

2.1.  Complex datatypes for Metadata

   Section 4.6.  (Element for Metadata Definitions) in the ForCES Model
   [RFC5812] limits the datatype use in metadata to only atomic types.
   Figure 1 shows the xml schema excerpt where ony typeRef and atomic
   are allowed for a metadata definition.

   However there are cases where complex metadata are used in the
   datapath, for example two simple use cases can be seen in the
   OpenFlow switch 1.1 [OpenFlowSpec1.1] and beyond:

   1.  The Action Set metadata is an array of actions descriptors, which
       traverses the processing pipeline along with the packet data.

   2.  When a packet is received from a controller it may be accompanied
       by a list of actions, as metadata, to be performed on it prior to
       being sent on the processing pipeline.  This list of actions is
       also an array.

   With this extension (Figure 2), complex data types are also allowed,
   specifically structs and arrays as metadata.  The key declarations
   are required to check for validity of content keys in arrays and
   componentIDs in structs.

       <xsd:complexType name="metadataDefsType">
         <xsd:sequence>
           <xsd:element name="metadataDef" maxOccurs="unbounded">
             <xsd:complexType>
               <xsd:sequence>
                 <xsd:element name="name" type="xsd:NMTOKEN"/>
                 <xsd:element ref="synopsis"/>
                 <xsd:element name="metadataID" type="xsd:integer"/>
                 <xsd:element ref="description" minOccurs="0"/>
                 <xsd:choice>
                   <xsd:element name="typeRef" type="typeRefNMTOKEN"/>
                   <xsd:element name="atomic" type="atomicType"/>
                 </xsd:choice>
               </xsd:sequence>
             </xsd:complexType>
           </xsd:element>
         </xsd:sequence>
       </xsd:complexType>

        Figure 1: Initial MetadataDefType Definition in the schema

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         <xsd:complexType name="metadataDefsType">
         <xsd:sequence>
           <xsd:element name="metadataDef" maxOccurs="unbounded">
             <xsd:complexType>
               <xsd:sequence>
                 <xsd:element name="name" type="xsd:NMTOKEN"/>
                 <xsd:element ref="synopsis"/>
                 <xsd:element name="metadataID" type="xsd:integer"/>
                 <xsd:element ref="description" minOccurs="0"/>
                 <xsd:choice>
                   <xsd:element name="typeRef" type="typeRefNMTOKEN"/>
                   <xsd:element name="atomic" type="atomicType"/>
                   <xsd:element name="array" type="arrayType">
                     <xsd:key name="contentKeyID1">
                       <xsd:selector xpath="lfb:contentKey"/>
                       <xsd:field xpath="@contentKeyID"/>
                     </xsd:key>
                   </xsd:element>
                   <xsd:element name="struct" type="structType">
                     <xsd:key name="structComponentID1">
                       <xsd:selector xpath="lfb:component"/>
                       <xsd:field xpath="@componentID"/>
                     </xsd:key>
                   </xsd:element>
                 </xsd:choice>
               </xsd:sequence>
             </xsd:complexType>
           </xsd:element>
         </xsd:sequence>
       </xsd:complexType>

          Figure 2: New MetadataDefType Definition for the schema

2.2.  Optional Default Value for Datatypes

   In the original schema, default values can only be defined for
   datatypes defined inside LFB components and not inside structures or
   arrays.  Therefore default values of datatypes that are constantly
   being reused, e.g. counters with default value of 0, have to be
   constantly respecified.  Additionally, datatypes inside complex
   datatypes cannot be defined with a default value, e.g. a counter
   inside a struct that has a default value of 0.

   This extension allows optionally to add default values to atomic and
   typeref types, whether they are as simple or complex datatypes.  A
   simple use case would be to have a struct component where one of the
   components is a counter which the default value would be zero.

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   This extension alters the definition of the typeDeclarationGroup in
   the XML schema from Figure 3 to Figure 4 to allow default values to
   TypeRef.

             <xsd:element name="typeRef" type="typeRefNMTOKEN"/>

    Figure 3: Initial Excerpt of typeDeclarationGroup Defintion in the
                                  schema

                 <xsd:sequence>
             <xsd:element name="typeRef" type="typeRefNMTOKEN"/>
               <xsd:element name="DefaultValue" type="xsd:token"
                     minOccurs="0"/>
                 </xsd:sequence>

      Figure 4: New Excerpt of typeDeclarationGroup Definition in the
                                  schema

   Additionally this document appends to the declaration of the
   AtomicType from Figure 5 to Figure 6 to allow default values to
   Atomic datatypes.  Note that both declarations include the new
   special value validation described in Section 2.7

    <xsd:complexType name="atomicType">
      <xsd:sequence>
        <xsd:element name="baseType" type="typeRefNMTOKEN"/>
        <xsd:element name="rangeRestriction" type="rangeRestrictionType"
         minOccurs="0"/>
        <xsd:element name="specialValues" type="specialValuesType"
         minOccurs="0">
          <!-- Extension -->
          <xsd:key name="SpecialValue">
            <xsd:selector xpath="specialValue"/>
            <xsd:field xpath="@value"/>
          </xsd:key>
          <!-- /Extension -->
        </xsd:element>
      </xsd:sequence>

     Figure 5: Initial Excerpt of AtomicType Definition in the schema

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    <xsd:complexType name="atomicType">
      <xsd:sequence>
        <xsd:element name="baseType" type="typeRefNMTOKEN"/>
        <xsd:element name="rangeRestriction" type="rangeRestrictionType"
         minOccurs="0"/>
        <xsd:element name="specialValues" type="specialValuesType"
         minOccurs="0">
          <!-- Extension -->
          <xsd:key name="SpecialValue">
            <xsd:selector xpath="specialValue"/>
            <xsd:field xpath="@value"/>
          </xsd:key>
          <!-- /Extension -->
        </xsd:element>
        <!-- Extension -->
        <xsd:element name="defaultValue" type="xsd:token"
          minOccurs="0"/>
        <!-- /Extension -->
      </xsd:sequence>

       Figure 6: New Excerpt of AtomicType Definition in the schema

   Examples of using default values is depicted in Figure 7.

            <dataTypeDef>
              <name>Counter Values</name>
              <synopsis>Example default values in struct</synopsis>
              <struct>
                <component componentID="1">
                  <name>GoodPacketCoutner</name>
                  <synopsis>A counter for good packets</synopsis>
                  <typeRef>uint32</typeRef>
                  <DefaultValue>0</DefaultValue>
                </component>
                <component componentID="2">
                  <name>BadPacketCoutner</name>
                  <synopsis>A counter for bad packets</synopsis>
                  <typeRef>uint32</typeRef>
                  <DefaultValue>0</DefaultValue>
                </component>
              </struct>
            </dataTypeDef>

               Figure 7: Example of optional default values

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2.3.  Optional Access Type for Structs

   In the original schema, the access type can only be defined on
   components of an LFB and not on components in structs or arrays.
   However when it's a struct datatype it is not possible to fine-tune
   access type per component in the struct.  A simple use case would be
   to have a read-write struct component where one of the components is
   a counter where the access-type could be read-reset or read-only,
   e.g. a read-reset or a read-only counter inside a struct.

   With this extension is it allowed to define the access type for a
   struct component either in the datatype definitions or in the LFB
   component definitions.

   When the optional access type for a struct component is defined it
   MUST override the access type of the struct.  The access type for a
   component in a capability is always read-only per [RFC5812].  If an
   access type is provided for a component in a capability it MUST be
   ignored.  Similarly if an access type is provided for a struct in a
   metadata it MUST be ignored.

   This extension alters the definition of the struct in the xml schema
   from Figure 8 to Figure 9.

       <xsd:complexType name="structType">
        <xsd:sequence>
          <xsd:element name="derivedFrom" type="typeRefNMTOKEN"
            minOccurs="0"/>
          <xsd:element name="component" maxOccurs="unbounded">
            <xsd:complexType>
              <xsd:sequence>
                <xsd:element name="name" type="xsd:NMTOKEN"/>
                <xsd:element ref="synopsis"/>
                <xsd:element ref="description" minOccurs="0"/>
                <xsd:element name="optional" minOccurs="0"/>
                <xsd:group ref="typeDeclarationGroup"/>
              </xsd:sequence>
              <xsd:attribute name="componentID" type="xsd:unsignedInt"
               use="required"/>
            </xsd:complexType>
          </xsd:element>
        </xsd:sequence>
      </xsd:complexType>

       Figure 8: Initial xml for the struct definition in the schema

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       <xsd:complexType name="structType">
        <xsd:sequence>
          <xsd:element name="derivedFrom" type="typeRefNMTOKEN"
            minOccurs="0"/>
          <xsd:element name="component" maxOccurs="unbounded">
            <xsd:complexType>
              <xsd:sequence>
                <xsd:element name="name" type="xsd:NMTOKEN"/>
                <xsd:element ref="synopsis"/>
                <xsd:element ref="description" minOccurs="0"/>
                <xsd:element name="optional" minOccurs="0"/>
                <xsd:group ref="typeDeclarationGroup"/>
              </xsd:sequence>
              <xsd:attribute name="access" use="optional"
                default="read-write">
                <xsd:simpleType>
                  <xsd:list itemType="accessModeType"/>
                </xsd:simpleType>
              </xsd:attribute>
              <xsd:attribute name="componentID" type="xsd:unsignedInt"
                use="required"/>
            </xsd:complexType>
          </xsd:element>
        </xsd:sequence>
      </xsd:complexType>

         Figure 9: New xml for the struct definition in the schema

   An example of using optional access types for structs can be depicted
   in Figure 10

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            <component componentID="1" access="read-write">
               <name>PacketFlows</name>
               <synopsis>Packet Flows, match and counter</synopsis>
               <struct>
                <component componentID="1">
                  <name>FlowMatch</name>
                  <synopsis>Flow Match</synopsis>
                  <typeRef>MatchType</typeRef>
                </component>
                <component componentID="2" access="read-only">
                  <name>MatchCounter</name>
                  <synopsis>Packets matching the flow match</synopsis>
                  <typeRef>uint32</typeRef>
                  <DefaultValue>0</DefaultValue>
                </component>
              </struct>
            </component>

          Figure 10: Example of optional access types for struct

2.4.  New Event Condition: BecomesEqualTo

   This extensions adds one more event condition in the model schema,
   that of BecomesEqualTo.  The difference between Greater Than and Less
   Than, is that when the value is exactly that of the BecomesEqualTo,
   the event is triggered.  This event condition is particularly useful
   when there is a need to monitor one or more states of an LFB or the
   FE.  For example in the CE High Availability (CEHA) [RFC7121] RFC it
   may be useful for the master CE to know which backup CEs have just
   become associated in order to connect to them and begin synchronizing
   the state of the FE.  The master CE could always poll for such
   information but getting such an event will speed up the process and
   the event may be useful in other cases as well for monitoring state.

   The event MUST be triggered only when the value of the targeted
   component becomes equal to the event condition value and MUST NOT
   generate events while the targeted component's value remains equal to
   the event condition's value.

   The BecomesEqualTo is appended to the schema as follows:

                       <xsd:element name="eventBecomesEqualTo"
                  substitutionGroup="eventCondition"/>

    Figure 11: New Excerpt of BecomesEqualTo event condition definition
                               in the schema

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   It can become useful for the CE to be notified when the state has
   changed once the BecomesEqualTo event has been triggered, e.g. the CE
   may need to know when a backup CE has lost association.  Such an
   event can be generated either by defining a second event on the same
   component, namely an Event Changed, or by simply reusing
   BecomesEqualTo and use event properties, in particular event
   hysteresis.  We append the following definition for the event
   hysteresis defined in section 4.8.5.2 in [RFC5812], with V being the
   hysteresis value:

   o  For an <eventBecomesEqualTo/> condition, after the last
      notification a new <eventBecomesEqualTo/> notification MUST be
      generated only one time once the value has changed by +/- V.

   For example using the value of 1 for V, will in effect create a
   singular event that will notify the CE that the value has changed by
   at least 1.

   A developer of a CE must also take into account to use count or time
   filtering to avoid being overrun by messages, e.g. in the case of
   rapid state changes.

2.5.  LFB Properties

   The current model definition specifies properties for components of
   LFBs.  Experience has shown that, at least for debug reasons, it
   would be useful to have statistics per LFB instance to monitor sent/
   received messages and errors in communication between CE and FE.
   These properties are read-only.

   In order to avoid ambiguity on protocol path semantics, this document
   defines that the LFB component with ID 0 specifically MUST target LFB
   properties and ID 0 MUST NOT be used for any component definition.
   This disallowment is backwards compatible as no known LFB definition
   uses LFB component with ID 0.  Any command with a path starting from
   LFB component 0 refers to LFB properties.  The following change in
   the xml schema disallows usage of LFB component 0:

              <xsd:attribute name="componentID" type="xsd:unsignedInt"
               use="required">

               Figure 12: Initial xml for LFB Component IDs

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                <!-- Extension Added restriction to component ID -->
                <xsd:attribute name="componentID" use="required">
                  <xsd:simpleType>
                    <xsd:restriction base="xsd:unsignedInt">
                      <xsd:minExclusive value="0"/>
                    </xsd:restriction>
                  </xsd:simpleType>
                </xsd:attribute>
                <!-- End of extension -->

    Figure 13: New xml for the disallowing usage of 0 as LFB Component

   The following datatype definitions are to be used as properties for
   LFB instances.

         <dataTypeDef>
            <name>LFBProperties</name>
            <synopsis>LFB Properties definition</synopsis>
            <struct>
               <component componentID="1">
                  <name>PacketsSentToCE</name>
                  <synopsis>Packets sent to CE</synopsis>
                  <typeRef>uint32</typeRef>
               </component>
               <component componentID="2">
                  <name>SentErrorPacketsToCE</name>
                  <synopsis>Error Packets sent to CE</synopsis>
                  <typeRef>uint32</typeRef>
               </component>
               <component componentID="3">
                  <name>BytesSentToCE</name>
                  <synopsis>Bytes sent to CE</synopsis>
                  <typeRef>uint32</typeRef>
               </component>
               <component componentID="4">
                  <name>SentErrorBytesToCE</name>
                  <synopsis>Error Bytes sent to CE</synopsis>
                  <typeRef>uint32</typeRef>
               </component>
               <component componentID="5">
                  <name>PacketsReceivedFromCE</name>
                  <synopsis>Packets received from CE</synopsis>
                  <typeRef>uint32</typeRef>
               </component>
               <component componentID="6">
                  <name>ReceivedErrorPacketsFromCE</name>
                  <synopsis>Error Packets received from CE</synopsis>
                  <typeRef>uint32</typeRef>

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               </component>
               <component componentID="7">
                  <name>BytesReceivedFromCE</name>
                  <synopsis>Bytesreceived from CE</synopsis>
                  <typeRef>uint32</typeRef>
               </component>
               <component componentID="8">
                  <name>ReceivedErrorBytesFromCE</name>
                  <synopsis>Error Bytes received from CE</synopsis>
                  <typeRef>uint32</typeRef>
               </component>
            </struct>
         </dataTypeDef>

                       Properties for LFB instances

2.6.  LFB class inheritance

   The ForCES model [RFC5812] allows inheritance for LFB classes.
   However the xml schema defines only the LFB class from which an LFB
   class may inherit.  Recent implementations have identified an issue
   where ambiguity rises when different versions of an LFB class exists.
   This document augments the derivedFrom part of the LFB class
   definition with an optional version attribute when the derivedFrom
   field is used.

   Having the version attribute as optional was a decision based on the
   need to maintain backwards compatibility with the XML schema defined
   in [RFC5812].  However if the version is omitted, then in the
   presence of multiple versions of the same LFB class, the derivedFrom
   will always select the latest version.

   This extension alters the definition of the derivedFrom in the xml
   schema from Figure 14 to Figure 15.

                       <xsd:element name="derivedFrom" minOccurs="0"/>

           Figure 14: Initial xml for the LFB class inheritance

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                       <xsd:element name="derivedFrom" minOccurs="0">
                         <xsd:complexType>
                           <xsd:simpleContent>
                             <xsd:extension base="xsd:NMTOKEN">
                               <xsd:attribute name="version"
                                 type="versionType" use="optional"/>
                             </xsd:extension>
                           </xsd:simpleContent>
                         </xsd:complexType>
                       </xsd:element>

             Figure 15: New xml for the LFB class inheritance

   An example of the use of the version attribute is given in Figure 16

                <derivedFrom version="1.0">EtherPHYCop</derivedFrom>

      Figure 16: Example of use of new xml for LFB class Inheritance

2.7.  Enhancing XML Validation

   As specified earlier this is not an extension but an enhancement of
   the schema to provide additional validation rules.  This includes
   adding new key declarations to provide uniqueness as defined by the
   ForCES Model [RFC5812].  Such validations work only on within the
   same xml file.

   The following validation rules have been introduced that did not
   exist in the original schema in [RFC5812]:

   1.  Each metadata ID must be unique.

   2.  LFB Class IDs must be unique.

   3.  Component ID, Capability ID and Event Base ID must be unique per
       LFB.

   4.  Event IDs must be unique per LFB.

   5.  Special Values in Atomic datatypes must be unique per atomic
       datatype.

3.  XML Extension Schema for LFB Class Library Documents

   This section includes the new XML Schema.  Note that the namespace
   number has been updated from 1.0 to 1.1

<?xml version="1.0" encoding="UTF-8"?>

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<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
   xmlns="urn:ietf:params:xml:ns:forces:lfbmodel:1.1"
   xmlns:lfb="urn:ietf:params:xml:ns:forces:lfbmodel:1.1"
   targetNamespace="urn:ietf:params:xml:ns:forces:lfbmodel:1.1"
   elementFormDefault="qualified" attributeFormDefault="unqualified">
   <xsd:annotation>
      <xsd:documentation xml:lang="en">
         Schema for Defining LFB Classes and associated types
         (frames, data types for LFB attributes, and metadata).
      </xsd:documentation>
   </xsd:annotation>
   <xsd:element name="description" type="xsd:string"/>
   <xsd:element name="synopsis" type="xsd:string"/>
   <!-- Document root element: LFBLibrary -->
   <xsd:element name="LFBLibrary">
      <xsd:complexType>
         <xsd:sequence>
            <xsd:element ref="description" minOccurs="0"/>
            <xsd:element name="load" type="loadType"
               minOccurs="0" maxOccurs="unbounded"/>
            <xsd:element name="frameDefs" type="frameDefsType"
               minOccurs="0"/>
            <xsd:element name="dataTypeDefs" type="dataTypeDefsType"
               minOccurs="0"/>
            <xsd:element name="metadataDefs" type="metadataDefsType"
               minOccurs="0"/>
            <xsd:element name="LFBClassDefs" type="LFBClassDefsType"
               minOccurs="0"/>
         </xsd:sequence>
         <xsd:attribute name="provides" type="xsd:Name"
            use="required"/>
      </xsd:complexType>
      <!-- Uniqueness constraints -->
      <xsd:key name="frame">
         <xsd:selector xpath="lfb:frameDefs/lfb:frameDef"/>
         <xsd:field xpath="lfb:name"/>
      </xsd:key>
      <xsd:key name="dataType">
         <xsd:selector xpath="lfb:dataTypeDefs/lfb:dataTypeDef"/>
         <xsd:field xpath="lfb:name"/>
      </xsd:key>
      <xsd:key name="metadataDef">
         <xsd:selector xpath="lfb:metadataDefs/lfb:metadataDef"/>
         <xsd:field xpath="lfb:name"/>
      </xsd:key>
      <xsd:key name="metadataDefID">
         <xsd:selector xpath="lfb:metadataDefs/lfb:metadataDef"/>
         <xsd:field xpath="lfb:metadataID"/>

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      </xsd:key>
      <xsd:key name="LFBClassDef">
         <xsd:selector xpath="lfb:LFBClassDefs/lfb:LFBClassDef"/>
         <xsd:field xpath="lfb:name"/>
      </xsd:key>
      <xsd:key name="LFBClassDefID">
         <xsd:selector xpath="lfb:LFBClassDefs/lfb:LFBClassDef"/>
         <xsd:field xpath="@LFBClassID"/>
      </xsd:key>
   </xsd:element>
   <xsd:complexType name="loadType">
      <xsd:attribute name="library" type="xsd:Name" use="required"/>
      <xsd:attribute name="location" type="xsd:anyURI"
         use="optional"/>
   </xsd:complexType>
   <xsd:complexType name="frameDefsType">
      <xsd:sequence>
         <xsd:element name="frameDef" maxOccurs="unbounded">
            <xsd:complexType>
               <xsd:sequence>
                  <xsd:element name="name" type="xsd:NMTOKEN"/>
                  <xsd:element ref="synopsis"/>
                  <xsd:element ref="description"
                     minOccurs="0"/>
               </xsd:sequence>
            </xsd:complexType>
         </xsd:element>
      </xsd:sequence>
   </xsd:complexType>
   <xsd:complexType name="dataTypeDefsType">
      <xsd:sequence>
         <xsd:element name="dataTypeDef" maxOccurs="unbounded">
            <xsd:complexType>
               <xsd:sequence>
                  <xsd:element name="name" type="xsd:NMTOKEN"/>
                  <xsd:element name="derivedFrom" type="xsd:NMTOKEN"
                     minOccurs="0"/>
                  <xsd:element ref="synopsis"/>
                  <xsd:element ref="description"
                     minOccurs="0"/>
                  <xsd:group ref="typeDeclarationGroup"/>
               </xsd:sequence>
            </xsd:complexType>
         </xsd:element>
      </xsd:sequence>
   </xsd:complexType>
   <!-- Predefined (built-in) atomic data-types are: char, uchar,
   int16, uint16, int32, uint32, int64, uint64, string[N], string,

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   byte[N], boolean, octetstring[N], float32, float64 -->
   <xsd:group name="typeDeclarationGroup">
      <xsd:choice>
         <!-- Extension -->
         <xsd:sequence>
            <!-- /Extension -->
            <xsd:element name="typeRef" type="typeRefNMTOKEN"/>
            <!-- Extension -->
            <xsd:element name="DefaultValue" type="xsd:token"
               minOccurs="0"/>
         </xsd:sequence>
         <!-- /Extension -->
         <xsd:element name="atomic" type="atomicType"/>
         <xsd:element name="array" type="arrayType">
            <!-- Extension -->
            <!--declare keys to have unique IDs -->
            <xsd:key name="contentKeyID">
               <xsd:selector xpath="lfb:contentKey"/>
               <xsd:field xpath="@contentKeyID"/>
            </xsd:key>
            <!-- /Extension -->
         </xsd:element>
         <xsd:element name="struct" type="structType">
            <!-- Extension -->
            <!-- key declaration to make componentIDs
              unique in a struct -->
            <xsd:key name="structComponentID">
               <xsd:selector xpath="lfb:component"/>
               <xsd:field xpath="@componentID"/>
            </xsd:key>
            <!-- /Extension -->
         </xsd:element>
         <xsd:element name="union" type="structType"/>
         <xsd:element name="alias" type="typeRefNMTOKEN"/>
      </xsd:choice>
   </xsd:group>
   <xsd:simpleType name="typeRefNMTOKEN">
      <xsd:restriction base="xsd:token">
         <xsd:pattern value="\c+"/>
         <xsd:pattern value="string\[\d+\]"/>
         <xsd:pattern value="byte\[\d+\]"/>
         <xsd:pattern value="octetstring\[\d+\]"/>
      </xsd:restriction>
   </xsd:simpleType>
   <xsd:complexType name="atomicType">
      <xsd:sequence>
         <xsd:element name="baseType" type="typeRefNMTOKEN"/>
         <xsd:element name="rangeRestriction"

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           type="rangeRestrictionType" minOccurs="0"/>
         <xsd:element name="specialValues" type="specialValuesType"
            minOccurs="0">
            <!-- Extension -->
            <xsd:key name="SpecialValue">
               <xsd:selector xpath="specialValue"/>
               <xsd:field xpath="@value"/>
            </xsd:key>
            <!-- /Extension -->
         </xsd:element>
         <!-- Extension -->
         <xsd:element name="defaultValue" type="xsd:token"
            minOccurs="0"/>
         <!-- /Extension -->
      </xsd:sequence>
   </xsd:complexType>
   <xsd:complexType name="rangeRestrictionType">
      <xsd:sequence>
         <xsd:element name="allowedRange" maxOccurs="unbounded">
            <xsd:complexType>
               <xsd:attribute name="min" type="xsd:integer"
                  use="required"/>
               <xsd:attribute name="max" type="xsd:integer"
                  use="required"/>
            </xsd:complexType>
         </xsd:element>
      </xsd:sequence>
   </xsd:complexType>
   <xsd:complexType name="specialValuesType">
      <xsd:sequence>
         <xsd:element name="specialValue" maxOccurs="unbounded">
            <xsd:complexType>
               <xsd:sequence>
                  <xsd:element name="name" type="xsd:NMTOKEN"/>
                  <xsd:element ref="synopsis"/>
               </xsd:sequence>
               <xsd:attribute name="value" type="xsd:token"/>
            </xsd:complexType>
         </xsd:element>
      </xsd:sequence>
   </xsd:complexType>
   <xsd:complexType name="arrayType">
      <xsd:sequence>
         <xsd:group ref="typeDeclarationGroup"/>
         <xsd:element name="contentKey" minOccurs="0"
            maxOccurs="unbounded">
            <xsd:complexType>
               <xsd:sequence>

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                  <xsd:element name="contentKeyField"
                     type="xsd:string" maxOccurs="unbounded"/>
               </xsd:sequence>
               <xsd:attribute name="contentKeyID" type="xsd:integer"
                  use="required"/>
            </xsd:complexType>
         </xsd:element>
      </xsd:sequence>
      <xsd:attribute name="type" use="optional" default="variable-size">
         <xsd:simpleType>
            <xsd:restriction base="xsd:string">
               <xsd:enumeration value="fixed-size"/>
               <xsd:enumeration value="variable-size"/>
            </xsd:restriction>
         </xsd:simpleType>
      </xsd:attribute>
      <xsd:attribute name="length" type="xsd:integer"
         use="optional"/>
      <xsd:attribute name="maxLength" type="xsd:integer"
         use="optional"/>
   </xsd:complexType>
   <xsd:complexType name="structType">
      <xsd:sequence>
         <xsd:element name="derivedFrom" type="typeRefNMTOKEN"
            minOccurs="0"/>
         <xsd:element name="component" maxOccurs="unbounded">
            <xsd:complexType>
               <xsd:sequence>
                  <xsd:element name="name" type="xsd:NMTOKEN"/>
                  <xsd:element ref="synopsis"/>
                  <xsd:element ref="description"
                     minOccurs="0"/>
                  <xsd:element name="optional" minOccurs="0"/>
                  <xsd:group ref="typeDeclarationGroup"/>
               </xsd:sequence>
               <xsd:attribute name="access" use="optional"
                  default="read-write">
                  <xsd:simpleType>
                     <xsd:list itemType="accessModeType"/>
                  </xsd:simpleType>
               </xsd:attribute>
               <xsd:attribute name="componentID" type="xsd:unsignedInt"
                  use="required"/>
            </xsd:complexType>
         </xsd:element>
      </xsd:sequence>
   </xsd:complexType>
   <xsd:complexType name="metadataDefsType">

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      <xsd:sequence>
         <xsd:element name="metadataDef" maxOccurs="unbounded">
            <xsd:complexType>
               <xsd:sequence>
                  <xsd:element name="name" type="xsd:NMTOKEN"/>
                  <xsd:element ref="synopsis"/>
                  <xsd:element name="metadataID" type="xsd:integer"/>
                  <xsd:element ref="description"
                     minOccurs="0"/>
                  <xsd:choice>
                     <xsd:element name="typeRef" type="typeRefNMTOKEN"/>
                     <xsd:element name="atomic" type="atomicType"/>
                     <!-- Extension -->
                     <xsd:element name="array" type="arrayType">
                        <!--declare keys to have unique IDs -->
                        <xsd:key name="contentKeyID1">
                           <xsd:selector xpath="lfb:contentKey"/>
                           <xsd:field xpath="@contentKeyID"/>
                        </xsd:key>
                        <!-- /Extension -->
                     </xsd:element>
                     <xsd:element name="struct" type="structType">
                        <!-- Extension -->
                        <!-- key declaration to make componentIDs
                           unique in a struct -->
                        <xsd:key name="structComponentID1">
                           <xsd:selector xpath="lfb:component"/>
                           <xsd:field xpath="@componentID"/>
                        </xsd:key>
                        <!-- /Extension -->
                     </xsd:element>
                  </xsd:choice>
               </xsd:sequence>
            </xsd:complexType>
         </xsd:element>
      </xsd:sequence>
   </xsd:complexType>
   <xsd:complexType name="LFBClassDefsType">
      <xsd:sequence>
         <xsd:element name="LFBClassDef" maxOccurs="unbounded">
            <xsd:complexType>
               <xsd:sequence>
                  <xsd:element name="name" type="xsd:NMTOKEN"/>
                  <xsd:element ref="synopsis"/>
                  <xsd:element name="version" type="versionType"/>
                  <xsd:element name="derivedFrom" minOccurs="0">
                    <xsd:complexType>
                      <xsd:simpleContent>

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                        <xsd:extension base="xsd:NMTOKEN">
                          <xsd:attribute name="version"
                            type="versionType" use="optional"/>
                        </xsd:extension>
                      </xsd:simpleContent>
                    </xsd:complexType>
                  </xsd:element>
                  <xsd:element name="inputPorts"
                   type="inputPortsType" minOccurs="0"/>
                  <xsd:element name="outputPorts"
                   type="outputPortsType" minOccurs="0"/>
                  <xsd:element name="components"
                   type="LFBComponentsType" minOccurs="0"/>
                  <xsd:element name="capabilities"
                   type="LFBCapabilitiesType" minOccurs="0"/>
                  <xsd:element name="events" type="eventsType"
                     minOccurs="0"/>
                  <xsd:element ref="description"
                     minOccurs="0"/>
               </xsd:sequence>
               <xsd:attribute name="LFBClassID" type="xsd:unsignedInt"
                  use="required"/>
            </xsd:complexType>
            <!-- Key constraint to ensure unique attribute names
            within a class: -->
            <xsd:key name="components">
               <xsd:selector xpath="lfb:components/lfb:component"/>
               <xsd:field xpath="lfb:name"/>
            </xsd:key>
            <xsd:key name="capabilities">
               <xsd:selector xpath="lfb:capabilities/lfb:capability"/>
               <xsd:field xpath="lfb:name"/>
            </xsd:key>
            <xsd:key name="events">
               <xsd:selector xpath="lfb:events/lfb:event"/>
               <xsd:field xpath="lfb:name"/>
            </xsd:key>
            <xsd:key name="eventsIDs">
               <xsd:selector xpath="lfb:events/lfb:event"/>
               <xsd:field xpath="@eventID"/>
            </xsd:key>
            <xsd:key name="componentIDs">
               <xsd:selector xpath="lfb:components/lfb:component"/>
               <xsd:field xpath="@componentID"/>
            </xsd:key>
            <xsd:key name="capabilityIDs">
               <xsd:selector xpath="lfb:capabilities/lfb:capability"/>
               <xsd:field xpath="@componentID"/>

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            </xsd:key>
            <xsd:key name="ComponentCapabilityComponentIDUniqueness">
               <xsd:selector
                  xpath="lfb:components/lfb:component|
                  lfb:capabilities/lfb:capability|lfb:events"/>
               <xsd:field xpath="@componentID|@baseID"/>
            </xsd:key>
         </xsd:element>
      </xsd:sequence>
   </xsd:complexType>
   <xsd:simpleType name="versionType">
      <xsd:restriction base="xsd:NMTOKEN">
         <xsd:pattern value="[1-9][0-9]*\.([1-9][0-9]*|0)"/>
      </xsd:restriction>
   </xsd:simpleType>
   <xsd:complexType name="inputPortsType">
      <xsd:sequence>
         <xsd:element name="inputPort" type="inputPortType"
            maxOccurs="unbounded"/>
      </xsd:sequence>
   </xsd:complexType>
   <xsd:complexType name="inputPortType">
      <xsd:sequence>
         <xsd:element name="name" type="xsd:NMTOKEN"/>
         <xsd:element ref="synopsis"/>
         <xsd:element name="expectation" type="portExpectationType"/>
         <xsd:element ref="description" minOccurs="0"/>
      </xsd:sequence>
      <xsd:attribute name="group" type="xsd:boolean"
         use="optional" default="0"/>
   </xsd:complexType>
   <xsd:complexType name="portExpectationType">
      <xsd:sequence>
         <xsd:element name="frameExpected" minOccurs="0">
            <xsd:complexType>
               <xsd:sequence>
                  <!-- ref must refer to a name of a defined
                    frame type -->
                  <xsd:element name="ref" type="xsd:string"
                     maxOccurs="unbounded"/>
               </xsd:sequence>
            </xsd:complexType>
         </xsd:element>
         <xsd:element name="metadataExpected" minOccurs="0">
            <xsd:complexType>
               <xsd:choice maxOccurs="unbounded">
                  <!--ref must refer to a name of a defined metadata-->
                  <xsd:element name="ref" type="metadataInputRefType"/>

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                  <xsd:element name="one-of"
                     type="metadataInputChoiceType"/>
               </xsd:choice>
            </xsd:complexType>
         </xsd:element>
      </xsd:sequence>
   </xsd:complexType>
   <xsd:complexType name="metadataInputChoiceType">
      <xsd:choice minOccurs="2" maxOccurs="unbounded">
         <!-- ref must refer to a name of a defined metadata -->
         <xsd:element name="ref" type="xsd:NMTOKEN"/>
         <xsd:element name="one-of" type="metadataInputChoiceType"/>
         <xsd:element name="metadataSet" type="metadataInputSetType"/>
      </xsd:choice>
   </xsd:complexType>
   <xsd:complexType name="metadataInputSetType">
      <xsd:choice minOccurs="2" maxOccurs="unbounded">
         <!-- ref must refer to a name of a defined metadata -->
         <xsd:element name="ref" type="metadataInputRefType"/>
         <xsd:element name="one-of" type="metadataInputChoiceType"/>
      </xsd:choice>
   </xsd:complexType>
   <xsd:complexType name="metadataInputRefType">
      <xsd:simpleContent>
         <xsd:extension base="xsd:NMTOKEN">
            <xsd:attribute name="dependency" use="optional"
               default="required">
               <xsd:simpleType>
                  <xsd:restriction base="xsd:string">
                     <xsd:enumeration value="required"/>
                     <xsd:enumeration value="optional"/>
                  </xsd:restriction>
               </xsd:simpleType>
            </xsd:attribute>
            <xsd:attribute name="defaultValue" type="xsd:token"
               use="optional"/>
         </xsd:extension>
      </xsd:simpleContent>
   </xsd:complexType>
   <xsd:complexType name="outputPortsType">
      <xsd:sequence>
         <xsd:element name="outputPort" type="outputPortType"
            maxOccurs="unbounded"/>
      </xsd:sequence>
   </xsd:complexType>
   <xsd:complexType name="outputPortType">
      <xsd:sequence>
         <xsd:element name="name" type="xsd:NMTOKEN"/>

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         <xsd:element ref="synopsis"/>
         <xsd:element name="product" type="portProductType"/>
         <xsd:element ref="description" minOccurs="0"/>
      </xsd:sequence>
      <xsd:attribute name="group" type="xsd:boolean"
         use="optional" default="0"/>
   </xsd:complexType>
   <xsd:complexType name="portProductType">
      <xsd:sequence>
         <xsd:element name="frameProduced" minOccurs="0">
            <xsd:complexType>
               <xsd:sequence>
                  <!-- ref must refer to a name of a defined
                     frame type -->
                  <xsd:element name="ref" type="xsd:NMTOKEN"
                     maxOccurs="unbounded"/>
               </xsd:sequence>
            </xsd:complexType>
         </xsd:element>
         <xsd:element name="metadataProduced" minOccurs="0">
            <xsd:complexType>
               <xsd:choice maxOccurs="unbounded">
                  <!-- ref must refer to a name of a
                     defined metadata -->
                  <xsd:element name="ref"
                     type="metadataOutputRefType"/>
                  <xsd:element name="one-of"
                     type="metadataOutputChoiceType"/>
               </xsd:choice>
            </xsd:complexType>
         </xsd:element>
      </xsd:sequence>
   </xsd:complexType>
   <xsd:complexType name="metadataOutputChoiceType">
      <xsd:choice minOccurs="2" maxOccurs="unbounded">
         <!-- ref must refer to a name of a defined metadata -->
         <xsd:element name="ref" type="xsd:NMTOKEN"/>
         <xsd:element name="one-of" type="metadataOutputChoiceType"/>
         <xsd:element name="metadataSet" type="metadataOutputSetType"/>
      </xsd:choice>
   </xsd:complexType>
   <xsd:complexType name="metadataOutputSetType">
      <xsd:choice minOccurs="2" maxOccurs="unbounded">
         <!-- ref must refer to a name of a defined metadata -->
         <xsd:element name="ref" type="metadataOutputRefType"/>
         <xsd:element name="one-of" type="metadataOutputChoiceType"/>
      </xsd:choice>
   </xsd:complexType>

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   <xsd:complexType name="metadataOutputRefType">
      <xsd:simpleContent>
         <xsd:extension base="xsd:NMTOKEN">
            <xsd:attribute name="availability" use="optional"
               default="unconditional">
               <xsd:simpleType>
                  <xsd:restriction base="xsd:string">
                     <xsd:enumeration value="unconditional"/>
                     <xsd:enumeration value="conditional"/>
                  </xsd:restriction>
               </xsd:simpleType>
            </xsd:attribute>
         </xsd:extension>
      </xsd:simpleContent>
   </xsd:complexType>
   <xsd:complexType name="LFBComponentsType">
      <xsd:sequence>
         <xsd:element name="component" maxOccurs="unbounded">
            <xsd:complexType>
               <xsd:sequence>
                  <xsd:element name="name" type="xsd:NMTOKEN"/>
                  <xsd:element ref="synopsis"/>
                  <xsd:element ref="description"
                     minOccurs="0"/>
                  <xsd:element name="optional" minOccurs="0"/>
                  <xsd:group ref="typeDeclarationGroup"/>
                  <xsd:element name="defaultValue" type="xsd:token"
                     minOccurs="0"/>
               </xsd:sequence>
               <xsd:attribute name="access" use="optional"
                  default="read-write">
                  <xsd:simpleType>
                     <xsd:list itemType="accessModeType"/>
                  </xsd:simpleType>
               </xsd:attribute>
               <!-- Extension Added restriction to component ID -->
               <xsd:attribute name="componentID" use="required">
                  <xsd:simpleType>
                     <xsd:restriction base="xsd:unsignedInt">
                        <xsd:minExclusive value="0"/>
                     </xsd:restriction>
                  </xsd:simpleType>
               </xsd:attribute>
               <!-- End of extension -->
            </xsd:complexType>
         </xsd:element>
      </xsd:sequence>
   </xsd:complexType>

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   <xsd:simpleType name="accessModeType">
      <xsd:restriction base="xsd:NMTOKEN">
         <xsd:enumeration value="read-only"/>
         <xsd:enumeration value="read-write"/>
         <xsd:enumeration value="write-only"/>
         <xsd:enumeration value="read-reset"/>
         <xsd:enumeration value="trigger-only"/>
      </xsd:restriction>
   </xsd:simpleType>
   <xsd:complexType name="LFBCapabilitiesType">
      <xsd:sequence>
         <xsd:element name="capability" maxOccurs="unbounded">
            <xsd:complexType>
               <xsd:sequence>
                  <xsd:element name="name" type="xsd:NMTOKEN"/>
                  <xsd:element ref="synopsis"/>
                  <xsd:element ref="description"
                     minOccurs="0"/>
                  <xsd:element name="optional" minOccurs="0"/>
                  <xsd:group ref="typeDeclarationGroup"/>
               </xsd:sequence>
               <xsd:attribute name="componentID" type="xsd:integer"
                  use="required"/>
            </xsd:complexType>
         </xsd:element>
      </xsd:sequence>
   </xsd:complexType>
   <xsd:complexType name="eventsType">
      <xsd:sequence>
         <xsd:element name="event" maxOccurs="unbounded">
            <xsd:complexType>
               <xsd:sequence>
                  <xsd:element name="name" type="xsd:NMTOKEN"/>
                  <xsd:element ref="synopsis"/>
                  <xsd:element name="eventTarget"
                    type="eventPathType"/>
                  <xsd:element ref="eventCondition"/>
                  <xsd:element name="eventReports"
                   type="eventReportsType" minOccurs="0"/>
                  <xsd:element ref="description"
                     minOccurs="0"/>
               </xsd:sequence>
               <xsd:attribute name="eventID" type="xsd:integer"
                  use="required"/>
            </xsd:complexType>
         </xsd:element>
      </xsd:sequence>
      <xsd:attribute name="baseID" type="xsd:integer"

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         use="optional"/>
   </xsd:complexType>
   <!-- the substitution group for the event conditions -->
   <xsd:element name="eventCondition" abstract="true"/>
   <xsd:element name="eventCreated"
    substitutionGroup="eventCondition"/>
   <xsd:element name="eventDeleted"
    substitutionGroup="eventCondition"/>
   <xsd:element name="eventChanged"
    substitutionGroup="eventCondition"/>
   <xsd:element name="eventGreaterThan"
    substitutionGroup="eventCondition"/>
   <xsd:element name="eventLessThan"
    substitutionGroup="eventCondition"/>
   <!-- Extension -->
   <xsd:element name="eventBecomesEqualTo"
      substitutionGroup="eventCondition"/>
   <!-- /Extension -->
   <xsd:complexType name="eventPathType">
      <xsd:sequence>
         <xsd:element ref="eventPathPart" maxOccurs="unbounded"/>
      </xsd:sequence>
   </xsd:complexType>
   <!-- the substitution group for the event path parts -->
   <xsd:element name="eventPathPart" type="xsd:string"
      abstract="true"/>
   <xsd:element name="eventField" type="xsd:string"
      substitutionGroup="eventPathPart"/>
   <xsd:element name="eventSubscript" type="xsd:string"
      substitutionGroup="eventPathPart"/>
   <xsd:complexType name="eventReportsType">
      <xsd:sequence>
         <xsd:element name="eventReport" type="eventPathType"
            maxOccurs="unbounded"/>
      </xsd:sequence>
   </xsd:complexType>
   <xsd:simpleType name="booleanType">
      <xsd:restriction base="xsd:string">
         <xsd:enumeration value="0"/>
         <xsd:enumeration value="1"/>
      </xsd:restriction>
   </xsd:simpleType>
</xsd:schema>

                           ForCES LFB XML Schema

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4.  Acknowledgements

   The author would like to acknowledge Joel Halpern, Jamal Hadi Salim
   and Dave Hood for their comments and discussion that helped shape
   this document in a better way.

5.  IANA Considerations

   IANA has registered a new XML namespace, as per the guidelines in RFC
   3688 [RFC3688].

   URI: The URI for this namespace is

   urn:ietf:params:xml:ns:forces:lfbmodel:1.1

   Registrant Contact: IESG

   XML: none, this is an XML namespace

6.  Security Considerations

   The changes described in this document have no effect on security as
   they are simply constructs to write XML library definitions.  Thus
   they have no effect on security semantics with the protocol and as
   such the security considerations that have been described in the
   ForCES Model RFC [RFC5812] apply to this document as well.

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              January 2004.

   [RFC5810]  Doria, A., Hadi Salim, J., Haas, R., Khosravi, H., Wang,
              W., Dong, L., Gopal, R., and J. Halpern, "Forwarding and
              Control Element Separation (ForCES) Protocol
              Specification", RFC 5810, March 2010.

   [RFC5812]  Halpern, J. and J. Hadi Salim, "Forwarding and Control
              Element Separation (ForCES) Forwarding Element Model", RFC
              5812, March 2010.

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   [RFC7121]  Ogawa, K., Wang, W., Haleplidis, E., and J. Hadi Salim,
              "High Availability within a Forwarding and Control Element
              Separation (ForCES) Network Element", RFC 7121, February
              2014.

7.2.  Informative References

   [OpenFlowSpec1.1]
              http://www.OpenFlow.org/, "The OpenFlow 1.1
              Specification.", <http://www.OpenFlow.org/documents/
              OpenFlow-spec-v1.1.0.pdf>.

Author's Address

   Evangelos Haleplidis
   University of Patras
   Department of Electrical and Computer Engineering
   Patras  26500
   Greece

   Email: ehalep@ece.upatras.gr

Haleplidis               Expires January 5, 2015               [Page 29]